Characteristics of "embryoid body" in human gonadal germ cell tumors.

The characteristics of so-called "embryoid body" appearing in gonadal germ cell tumors were studied histologically and immunohistochemically on serial sections of three cases (one ovary and two testes). The embryoid bodies were usually observed to be contiguous with immature or mature intestinal ducts, hepatic nests, or epidermal cell nests on serial sections, though they appeared to be isolated in one section. The "amniotic cavity"-like structure of embryoid body was continuous with intestinal duct, and rarely with squamous cell nests, while the "yolk sac" was continuous with hepatic tissue. In these immature or mature structures, differentiation was always found independently of "disc," and portions of "ectoderm" and "endoderm" remained less differentiated in comparison with others. These findings were in contrast with a normal embryo in which immature and/or mature structures are derived from the embryonic disc. The amniotic cavity connected frequently with yolk sac. From the present results, the embryoid body is not considered to be a real or teratomatous embryo, but only a product during a divergent differentiation into intestine and liver from the plastic epithelium, which seems to be derived from an embryonic gut.